Fiber curl is the inherent tendency of a length of uncoated fiber to exhibit some degree of curvature. Heretofore, such curvature has not presented a problem inasmuch as connections to or splicing of, most optical fibers has been on an individual fiber basis, generally using active alignment devices. However, because of the enormous increase in the use of optical fibers for communications signal transmissions, it has been necessary to find ways of treating, e.g., splicing, fibers en masse. Thus, there have evolved passive alignment technologies which optimize fiber alignment for groups of fibers, such as ribbon cables. The random orientation of the curvature of individual fibers within such a ribbon can cause misalignment of fibers in the mass splicing operation. The problem of such misalignment is exacerbated in the field, where the technician lacks the necessary equipment to correct for it. As a consequence, fiber manufactures have sought ways to quantify and control the amount of curvature in their fibers in order that end users of the fiber can be assured that fiber curl will not adversely impact the splicing efficiency or yields of their mass splices. In addition, monitoring of fiber curl during the manufacturing process helps to supply a feedback to the operators of the up-stream processes in the fiber fabrication, thus making it possible to minimize yield losses resulting from too great fiber curl by adjusting these processes to reduce curl.
As a prerequisite for quantiignd and controlling fiber curl, a method for measuring such curl is necessary. In the prior art there have been numerous arrangements for determining or, more particularly, measuring fiber curl, as exemplified by one such method as shown and described in an article entitled "Straightening Out the Fiber Curl Problem", by J. Farro and K. Erng, Photonics Spectra, September 1993, at pages 102 through 108. The apparatus shown therein comprises a V-groove holder such as a vacuum chuck, or a ferrule, for holding the fiber under test on a constant axis that allows rotation of the fiber through three hundred and sixty degrees (360.degree.). The fiber may be rotated either manually or by a stepping motor arrangement which rotates a fiber holder relative to the ferrule or vacuum chuck. Fiber deflection from the axis as it is rotated is measured by, for example, a viewing microscope or some type of optical measuring instrument, such as a laser micrometer. Additionally, an image analysis system, a video camera and monitor, or a video analyzer and computer may be used. To make the measurements, the fiber is placed in the ferrule or vacuum chuck with a ten to twenty millimeter (10-20 mm) overhang. As the fiber is rotated, as by the stepping motor, preferably in fifteen degree (15.degree.) increments, the magnitude of the fiber excursions is measured. The data obtained are fitted to a sine function to determine peak-to-peak amplitude, which indicates, by proper calculation, the radius of curvature of the fiber. With the overhang known, and the maximum deflection measured, the fiber's radius of curvature can be obtained from a simple circular model. Such an arrangement has been used to determine the radius of curvature or of large numbers of fibers with good or satisfactory accuracy. However, while the method discussed, or variations thereof, is in wide use because of its relative simplicity, the apparatus presents certain problems which, in a production environment, can be costly. For example, the vacuum chuck constantly draws dirt particles into its fiber holding groove. This problem is mentioned in the foregoing Farro and Ernig article. The apparatus must be shut down periodically while the chuck is cleaned. As a result of dirt accumulating in the grooves, the vacuums' force decreases and the fiber is not held at a constant axis, thereby inducing measurement errors. Additionally, each time a new fiber is to be introduced into the apparatus, the vacuum force must be cut off while the fiber is placed in the chuck groove.
The use of a ferrule in place of a vacuum chuck introduces different problems. The fiber must be inserted slowly and rotated gently during insertion to avoid breakage, which is a tedious, tiring and slow process for the operator. If a fiber break occurs within the ferrule, it is quite difficult to remove it because of the extremely small diameters involved. Thus, each of the accepted methods of holding the fiber presents its own problems, with the net result of slowdowns and interruptions in the production process.